1. Field of the Invention
The present invention relates to a process and to a plant for the gasification of biomass for production of fuel gases that may be used directly for combustion, in the case of low BTU gas, or be treated to form medium BTU substitute natural gas useful for industrial processes (for drying, steam production, space heating and lighting, conversion into electrical energy, etc). The invention constitutes also a solution to the waste disposal problem.
The term "biomass", as used in this description and the appended claims, includes solid wastes, peat, coal, wood residues such as wood chips and sawdust, organic and inorganic residues including solid and semi-solid carboneous materials as well as shale and cellulosic fibers.
Also, the expression "oxygen-containing gas" is to be understood to mean either air or enriched air or oxygen.
2. Description of the Prior Art
The Applicants are well aware that quite extensive research, development and experimental work has been made to convert waste material into fuel gas useful directly for combustion or for conversion into industrial process gases. A typical and very pertinent document, in this respect, is U.S. Pat. No. 4,592,762 of June 2nd. 1986. However, the process disclosed in this patent remains applicable only on an experimental stage as many parameters involved do not permit a large scale profitable operation. Thus, while it is said that the moisture content of the biomass may be reduced to 5% to 50%, it is added that if the reduction is from 5% to 40%, steam has to be added to the fluidized bed which, of course, produces a highly moist output gas which has to be more heavily treated either for direct combustion or for use in industrial processes in general. Additionally, the fluidized bed is fed, according to this patented process, intermittently which affects its efficiency and shows that the process is still in the experimental stage. Notable also is the fact that while the disclosure of the patent mentions feeding the biomass into the fluidized bed, the precise location where feeding is to be made is not given which, again, may be detrimental to the proper and efficient functioning of the bed.
In general, the literature known to the Applicants is unable to teach a process and disclose a plant suitable to produce low and medium BTU gases on an industrial scale, that is having a high yield of BTU gases recuperated at a relatively low cost.